Hydraulic dimpling unit



Jan. 8, `1952 W. J. HOFFMAN HYDRAULIC DIMPLING UNIT Filed Aug. 25. 1948 /7 T01@ WST Patented Jan. 8, 1952 Utur'r-ED STATES PATENT ofFFlc-E HYDRAULIC nnvneLnmsf UNIT William J. Hoffman, Babylon, N. Y. l'ApplicationArglist-'25, 194s, serial No; 46,163

(c1.rv 153-5-21) l comms. I

n This invention relates -tc improvementsinfdimpling machines.

Itis an object ofthe invention to provide-an improvedl dimplingmachine which permitsl reduction inY oil canning of the'sheetmetal being dimpled, andv also permits the formation offa `dirnple'with a sharp corner.

'A further object is-to-Yprovide a dimming-"machine which facilitates hot dimpling.

In dimpling, the sheet metal, -in which a rivet rhole-has"previouslyheen bored, is'subjected to the action of a cooperating punch and die, by

means-offwhich the metalaround the rivet hole formed so as to be concave on one side-andvcom vex on the other. The punchr may he surround- `ed Aby apressure padand it has beenA knownvto support such pads resiliently as by means of rubber or springs. However, the lpressure conveniently obtainable has been too low to grip the metal around the rivethole sufficiently toprevent movement thereof. y As a resultv warping of the metal around the rivet'ho1e, commonly referred to as oil canning, tends to occur and the rim of the concave side of the dimple tends not vto' be as sharp or definite irl-'outline as might be desired. The present invention Y provides a -hy- N'draulic cushionAv for thef-pad infaedimpling machineggripping the metal around-the punch-with v--su'cient force to prevent' oil canning-land to forma sharp corner on the dimple.

Where hot dimpling is performedgthe'- inven- `tionl also Iprovides for reliably maintaining the heat of lthe metal to the desired degree.

For afull understanding of the invention, a

detaileddescription off-afdi'mpling machine em- 5 bodying the invention in a preferred formA will now vhe given in connection with the accompanying drawing, and the features forming the invention will then be specifically pointed out in n the appended claims.

In the drawing;

Figure 1y is aschematic View of amachine einbodying the invention in a preferred form of em-` embodiment;

-Fignre'a is a-vew yin vertical Sfstwmjand 911 v"an enlawgedV Scale, ofY the parts cooperating t0 form the dimple; n

``Figure sis a-riew'similartc Figure 2fb1tsh0w= .ing the parts. in' adifferent position; and

Figure 4 is a plan View of the pad of Figures 2 and I3- shown schematically in Figure 1, the dimpling machine comprises a 4squeezer or compression riveter of generally known type, in which the yoke or frame A carries operating mechanism B land held in the desiredlposition of adjustment by alocl:v nut 5.

A cylinderdesignatedvr generally `Icy the numeral 'hasaninner bore 'l cooperating with the pisten @and vsealed thereto by meansfof an O`ring SIcar'r'ied in a' groove in the piston; -UpWa-rd movement ofthe cylinder 6 yis llimited by means ofan annular capi), screwed thereon and having a' shoulder or lip lil for eng-aging funder the piston as indicated.

The cylinder 611s formed with asocketfor holdingthe pad E'and the punch Dissupported by the piston 3. For` this purpose piston lhas'a vcylindrical!upper projection ll'ftting withina bore l2 of the cylinder and sealedV thereto'by fan- Gering i3 carried ina `groove in the latter.

The projection Il, in turn, has a central socket i l5 which holds vthepunchD, the enlarged shank I6 thereof fitting Withinthe socket-as indicated.

The punch` DY further compris-es a reduced section I1 fitting within a corresponding central bore of the pad E, a conical shoulder I8 for forming the dimple and La tip I9 which passes through the 'previouslybored rivet holein the sheet beingdim.- pled.

n For hot dimpling, the 'pad E may be heated as V`by means of 'heater elements 20' within it. Where hot'dimpling is not being' done, these heater elements may be omitted.

The die C is formed with a central aperture comprising a bore E22, which receives the tip I9 ofthe punch,- and a conically flared mouth 23.

vwhich, cooperates with the conical shoulder f 8 0f the punch tov fcrmthe dimple. yThe annular surface 24 ofthe die vsurrounding the opening cooperates with the pad E tonoidgtnemetaibeing "formed-las later described. The surfacel'ldf is substantially flat but is slightly tapered. The extent of taper is exaggerated in the drawing and will normally be of the order of one degree, rang: in g from half a degree to two degrees depending upon the material `being worked. An electric heater 25 may be provided for heating the die,

cylinder 6 and oil line 3! will be filled with oilV at all times and the accumulator 32 will be filled half way up, or up to the level of the p-lug 35. Pressure is supplied by introducing air from a pressure bottle or other convenient source through the fitting 34, so as to maintain a pressure of about 600 p. s. i. draulic pressure within the cylinder, acting against the piston 3 (which is stationary) forces the cylinder up into the position of Figure 2 with the lip Il) engaging under the piston. When the die comes down, as indicated in Figure 3, the pad E and cylinder 6 are forced down against the Vhydraulic pressure. Further movement forms the dimple.

The sheet metal G, as indicatedv in Figure 3, will normally have a line or other pattern of rivet holes of diameter corresponding to the tip i9 of the punch, preformed in it. For forming the dimple, one of these holes is placed over the tip I9 of the punch, the parts being in the position of Figure 2. The die C now comes down and the annular surface 24 will engage the metal G first, forcing it against'the pad E and thus forcing the pad E downwardly against the hydraulic pressure within the cylinder. The conical portion I8 of the punch being below the surface of the pad at this time, the rst action which occurs f will accordingly be the gripping of the sheet between the die and the pad. FurtherV movement of the die forces the pad still further down, exposing the conical portion erof the punch, and forming the metal into a dimplebetween this conical portion I8 and the `flare 23 of the die.V

By reason of the fact that the sheet metal G is firmly gripped between the die C and the pad E at the time when the punch D is forming the dimple, the movement of the metal around the dimple is prevented, thus preventing oil canning and forming an exceptionally sharp corner around the dimple. Y f In a typical installation the total pressure applied to the cylinder by the hydraulic fluid may be approximately two tons. As the sheet being ,dimpled is forced down by the die so as tor unseat the cylinder, this pressure is carried by the annular surface 24, which may be about .15 square inch in area or thereabouts, resulting in a gripping pressure on the metal, neglecting the taper of the surface 24, of the order of 25,000 pounds per square inch. The actual effective gripping pressure which is exerted maybe higher than this due to the slight taper of the surface 24. It will be apparent that the invention provides for applying gripping pressures between die and pad of' any usable magnitude whichmay be desired, and that the limiting factor on the gripping pres- As will be apparent,the `hysure values which are used may be merely the ability of the metal around the dimple to resist undesirable permanent change of form.

While the total travel of the cylinder 6 against the hydraulic pressure may be of the order of one-sixteenth of an inch or thereabouts, the pad pressure may be sufficient so that as much as one-half the power consumed by the machine is utilized in overcoming the pad resistance. It is found that the'hydraulicsystem as constructed is Vcapable of dissipating this power without undue heating.

' As will be apparent to those skilled in the art, provision for dimples Vof different sizes may be' made by substituting sets of dies, punches and pads, C, D and E, having different dimensions of coacting parts but fitting within the sockets provided therefor as indicated in the drawing.

Where hot dimpling is done, the strong holding pressure between the die C and the pad D provides excellent contact between these elements and the sheet surrounding the dimple so that the best possible heat transfer conditions are obtained. Thus it is possible to heat the sheet adjacent the rivet hole to the desired temperature in the shortest possible time and maintain it at such temperature while the dimple is being formed. The very firm gripping of the sheet also eliminates difficulties that might otherwise arise due to, thermal expansion of the metal when heated. In hot dimpling the cycle of operations is the same as in the cold dimplingpreviously described, but the down stroke of the die C is interrupted for a sufficient length of time just before the punch D comes into operation to permit bringing the metal to the desired temperature for forming the dimple.

Y What is claimed is:

1. In a dimpling machine, the combination with a movable die and cooperating punch of a stationary piston carrying a projection having a socket for supporting the punch, a movable cylinder cooperating with the piston 'and projection, the cylinder having a socket for supporting a pad surrounding the punch, and means for maintaining hydraulic pressure within the cylinder.

2. In a dimpling machine, the combination with a movable die l,and cooperating punch of a stationary piston carrying a projection having a socket for supporting the punch, a movable cylinder cooperating with the piston and proj ection, the cylinder having a socket for supporting a pad surrounding the punch, an accumulator and a pressure line connecting it to the cylinder for maintaining hydraulic pressure within the cylinder.v l

WILLIAM J. HOFFMAN.

'REFERENCES CITED The following references are of record inet-he i-lle of this patent:

UNITED STATES PATENTS 2,453,762 Schwartz' Ney. 16', 1948 

